The present invention relates generally to the batch fabrication of sliders which carry magnetoresistive (MR) and/or inductive transducers for data storage applications. More particularly, the present invention relates to the measurement of electrical lap guide (ELG) resistors which guide the lapping process such that the head sliders in a row or bar are machined to a specified transducer height.
Magnetic read/write transducers are produced using thin film deposition techniques. In a typical process, an array of transducers are formed on a common substrate. The substrate is sliced to produce bars, with one row of transducers in a side-by-side pattern on each bar. The bars are then machined or lapped to establish a desired MR transducer height (sometimes referred to as a stripe height SH) or a desired inductive transducer height (sometimes referred to as a throat height TH). After the air bearing surface pattern is formed on the bars, the bars are diced to produce individual head sliders which contain the magnetic transducers.
In order to establish adequate performance for high efficiency recording heads, it is desired to achieve the specified transducer height with very tight tolerance. ELGs for this and other purposes are well known in the art. See for example, U.S. Pat. No. 5,023,991 entitled ELECTRICAL GUIDE FOR TIGHT TOLERANCE MACHINING, which issued to Alan Smith on Jun. 18, 1991. One common practice is to use ELGs and a feedback controlled bending mechanism to form a closed-loop lapping process. ELG measurement accuracy, noise and resolution directly affect finished slider SH and TH variation. As the data storage industry is continuously driven by higher density and lower cost requirements, the transducer height tolerance continues to decrease, while the number of head sliders per bar increases, leading to thinner and more flexible bars. To maintain and improve transducer height control during the lapping process, more accurate ELG measurement and monitoring techniques are required.
ELG's typically include three resistive components, but can contain a greater or lesser number if desired. Frequently, as many as 14 ELGs are included per bar. Therefore, a great number of resistances must be measured during lapping. Conventionally, data acquisition units (DAUs) for measuring the resistances of the large number of ELG components on a bar have included a single current source, a multiplexer, and a signal processing channel. To measure the resistance of an individual ELG resistive component, the single current source is directed by the multiplexer to excite the component. The corresponding voltage signal is connected to the signal processing channel by the multiplexer and is amplified, filtered and digitized The digitized resistance reading is then stored in the memory of the control computer. This procedure is repeated through time multiplexing, with the single current source exciting one resistive element at time, through switching or multiplexing, to read all of the ELG resistive elements.
These conventional DAU measurement systems and techniques introduce a number of problems. First, ELG resistance readings using conventional DAUs are not independent of other ELG resistance readings. To make the measurements at a desired sampling rate, the current source, voltmeter and filter have to be switched from resistive element to resistive element through multiplexing. Since the current source and the filters need time to settle after switching from one ELG measurement to the next, significant quantities of noise are introduced into the measurement signal if too many resistive elements are monitored, thus limiting the time available. Other sources of noise which effect the measurement accuracy are caused by the mechanical bending portions of the system. These and other disadvantages of prior art lapping systems are eliminated or reduced by the present invention.